1. Field of the Invention
The present invention relates to an optimized power package for an electrical device; and, more particularly, to an optimized power package for an electrical device of an Electronic Control Unit (ECU) in an Electric Power Steering (EPS) system, in which it is possible to expand areas of a PCB layer and an LTCC layer, to enhance the freedom degree of design of the PCB and LTCC layers, and to reduce a size of the entire case.
2. Description of the Related Art
With the recent development of electrical device modules, users have gradually demanded for miniaturization and high-performance of the modules. In line with the trend, there has been also a need of miniaturization and high-performance of parts used in the modules.
However, in the prior art, since parts to be mounted are positioned on a planar Printed Circuit Board (PCB), there has been a limit to the number of the mounted parts on the planar PCB. Further, when an over-current flows to a path line on the PCB, high-temperature heat is produced due to miss-matching, which results in low reliability.
In order to solve these problems, a Low Temperature Co-fired Ceramics (LTCC) has been used. An LTCC element is known generically as an element manufactured by co-firing both of a metal electrode and a ceramic substrate at a temperature of less than 1,000° C. lowered by 200° C. or higher than a firing temperature widely used at ceramics-firing.
The LTCC element provides higher mounting density and more effectively emits heat generated in an IC, in comparison with the PCB, so it is being used as a passive element for high-frequency communication and a control module for an electrical device.
However, as an LTCC is very expensive, costs to manufacture a substrate with the LTCC is increased. Thus, as shown in FIG. 1, there has been presented a proposal of using an LTCC layer 30 together with a PCB layer 20. The LTCC layer 30 and PCB layer 20 are positioned on the substrate 10 and interconnected with the wire bonding 40. However, whenever the LTCC layer 30 together with the PCB layer 20 are used on the same plane, areas of the LTCC 30 and PCB 20 layers become relatively reduced, which results in restriction on not only its design, but the number of elements to be mounted as well.
An electrically-powered EPS system electrically controls steering torque of a handle depending on traveling speed of a vehicle. In particular, the electrically-powered EPS system allows the steering torque to be light at parking or low-speed traveling, and allows the steering torque to be heavy at high-speed traveling, thereby enabling the driver to stably travel at high speed. That is, the EPS system aims to improve vehicle's mileage and cope with an electrical vehicle.
Advantages of the EPS system include reduction in vehicle's weight, and improvement (3 to 5%) of vehicle's mileage due to prevention of power loss. Moreover, the EPS system has advantages of less consumed maintenance and environmentally-friendly characteristics. Furthermore, as for other advantages of the EPS system, there are miniaturization and improved assembly due to a reduction in the number of parts used in the EPS, accurate control of the steering torque for each speed of the vehicle, improvement of steering performance resulting from improved stability of high-speed traveling, and so.
The EPS system includes three circuits around a micro computer; an input circuit of vehicle's speeds and two-based steering torques, a driving circuit of a motor, and a detecting/monitoring circuit of a motor current and a voltage. In the EPS system, the micro computer determines an assist amount by torque and vehicle-speed signals and calculates location of a rotor (rotation sensor) and reference currents, which flow to each of three phases by actual currents of the motor. Then, a three phase-Pulse-Width Modulation (PWM) circuit outputs signals to each phase of the motor, and thus the motor is driven while the power steering is achieved.
In particular, because interference between other parts is caused when an ECU of an EPS system is mounted on a vehicle, its housing becomes gradually downsized.
In addition, the housing's size is definitely set at an initial stage, so parts such as a connector, and so on are designed and arranged on a PCB layer and an LTCC layer positioned at defined areas in a two-dimensional plane. Therefore, a reduction in areas of the LTCC and PCB layers reduces a path line on which currents flow, as well as the number of the parts to be mounted. Therefore, flow of over-currents to the reduced path line results in mis-matching. This is because, since a line width of 0.1 mm is required per a current of 1 A, a path line width of about 10 cm is required for a current of 90 A. This means that it is impossible to properly implement a path line on a conventional PCB layer.
Additionally, it is necessary to secure such a space that a number of parts can be mounted on the LTCC layer, and such a minimum area that a bonding pad signal-connected to the PCB layer is provided on the LTCC layer. However, in case where the LTCC and PCB layers are implemented on the same plane, it is difficult to secure the mounting space and the minimum area.
Moreover, in case where the LTCC layer has a narrow area, a defective rate is increased at wire-bonding.